Failure testing on 4130 tubing

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This is 4130, 1.25" tubing with 0.35 wall thickness.The filler is ER 70-S2 0.35.The idea is that I want to test my weld skill and make sure the stuff I build is safe.  ( I mostly plan to build bicycles ).Do you guys think the failure occurred at the proper point?  As you may guess the failure was triggered by jacking the structure apart.Please let me know your thoughts.
Reply:Interesting device you came up with. I can't share any knowledge on 4130 but I'd also like to hear what someone with more experience might say.
Reply:How much effort did it take to seperate it like that?  I know it's going to be a subjective matter for the answer.  In the future, I would recommend mounting one end in a vise somehow and using a torque wrench (the type with a pointer that shows how much torque you applying) to load the nut.  This will at least give you a subjective number for future testing. Originally Posted by SundownIIIDon't get me wrong.  They are just as ill informed about politics as they are about welding, they just post more on that subject.
Reply:Looks to me like you have to much heat for 4130."Liberalism is a mental disorder" Dr. Savage
Reply:What amperage were you running?
Reply:The welds themselves look like they need a lot more work to become consistent.  The best of the bunch looks like the one bottom right and it still has a ways  to go. They look "cold", but I see a lot of "heat" sign on the tube. I'm thinking the tube failed in the HAZ, possibly from overheating, or maybe poor weld procedure. Did you quench this by any chance?Some general comments. I see a lot of guys jumping straight to tube work with tig who have never learned to run basic beads on flat plate. If you can not run decent beads on flat plate in all positions, tube will be extremely difficult to do well and it gets exponentially more difficult to do small dia tube. It's compounded even more, when you want to do thin tube. Looking at your beads makes me think you might fall in this category. Can you make nice consistent beads on flat plate this thin? The majority of guys can not. Tossing tube into the mix reduces the number of people who can make good welds. The reason I think you may not have the needed basic skills is that I'd expect someone with the hours needed to be at this point to have better beads in general, and know just how poor these beads look.If you can not run beads on flat plate, you need to go back to the basics and learn how, starting with say 1/8" and then when you can do that get progressively thinner, then going to  "large" heavier wall tube. Trying to skip to chapter 30 will not give you the results you are looking for. It would not at all surprise me to see someone needing over a thousand hours of good practice to pull these beads off successfully..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by jmtebbensHow much effort did it take to seperate it like that?  I know it's going to be a subjective matter for the answer.  In the future, I would recommend mounting one end in a vise somehow and using a torque wrench (the type with a pointer that shows how much torque you applying) to load the nut.  This will at least give you a subjective number for future testing.
Reply:Hi, Mark. I'd expect the failure to start closer to the weld toe. Further away indicates a HAZ that's too large. I'd agree that failures generally occur in the HAZ rather than the weld itself (in a properly designed and executed joint) in steel tubing. When I was doing warranty and service work for ti bikes, we could usually trace a brittle weld fracture (crack propagation starting in the weld itself) to a bad purge or other types of contamination as you would expect. Contaminated titanium is about as brittle as it gets. We never saw a failure like that in a steel bike though. The steel failures were usually from a crash or driving the bike into the garage on top of the car and the failure would be a 1/16" or so from the weld toe.Hope that helps!
Reply:Thanks Mike, I was hoping you would comment.  I clean the tubing with sanding flap wheel, soapy water, alcohol and a wire brush.  My shielding is a #10 gas lens with argon at 15 cfh.  The welds are not super pretty but they are clean and not contaminated.  I am also working on my welding to reduce the HAZ area and make the welds more visually consistent.  My guess is that a fatigue failure test would occur closer to the weld.  I am going to be doing more of these test samples and am working up a design for a simple fatigue cycle testing machine.  My thinking is that the basics of the test setup are sound because it gives me a way to establish a "safety factor".  When I build the fatigue cycle testing I can take the approach one step further.
Reply:I would agree with Walt over on MTBR that most of the frame failures I've seen are fatigue related and there isn't a lot to be learned from the type of test you did once the welds are up to snuff. The inconsistencies in the bead act as stress risers and those can lead to crack initiation after X number of cycles. The smoother you can blend the toe into the tube and the smoother you can make the fillet (flat to slightly concave), the better off you'll be.
Reply:Ya, I agree with Walt as well and will be spending a lot of time under the hood with practice welds.  The nice thing about the test structure is that it is simple to build and good practice.  My general plan is to build a bunch of these simple test structures in a consistent design.  At some point I will be creating a fatigue testing machine and as such it will be nice to have an inventory of weld test samples.
Reply:Good stuff. Only you can decide what's best for you in terms of testing. Have some fun along the way too.
Reply:Yes, failure should be in the HAZ.Your HAZ looks really big.Normalizing-after welding allows for more stretching (elongation);as opposed to a sharp, brittle, cracking failure seen here.That's 'why?' it really helps, especially on thin wall 4000 series.It's time for Makoman to chime in, here.Blackbird
Reply:Your HAZ looks large, you may need to work faster.Without knowing how much force you used it's hard to determine exactly "how much too slow" you are going.How did it break?  Did it pop apart, snap apart, or tear apart?  & at what pressure?If you subjected it to 80,000 lbs /sq in than it's totally ok.If it's 15,000, not so much..Buy American, or don't whine when you end up on the bread line.
Reply:Originally Posted by WeldingMachineYour HAZ looks large, you may need to work faster.Without knowing how much force you used it's hard to determine exactly "how much too slow" you are going.How did it break?  Did it pop apart, snap apart, or tear apart?  & at what pressure?If you subjected it to 80,000 lbs /sq in than it's totally ok.If it's 15,000, not so much..
Reply:Well lets see some more, keep practicing and show us your progress..  You could try a bit larger filler as well, that may be part of your problem...HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:That's exactly where I would have guessed it would fail. The weld itself is a much thicker, stiffer, and better tied in location, so even if the metal isnt as stong there it's not going to break there first. Right outside the weld where the thin tube has been heated (and lost it's temper so to speak) is going to be weaker than anywhere else.Welding/Fab Pics: www.UtahWeld.com
Reply:You can do testing like that with accurate load sensing and the results are likely to have a large scatter plot. Best to control one thing at a time... pick -> design, material, process.Then, when and if, you do tear it apart there is more to look at than just the welding part. The steel mill has tolerance, the rolling process has tolerance, the seam weld, and on and on. Stuff can creep in most anywhere.I up-sized the picture and see what looks like a "tooth" (arrow), this is good. I also think the failure is not exactly a straight line perpendicular to  tension. The HAZ is affected by heat input, slower travel = HAZ farther away and wider, faster travel = closer HAZ and narrow. Wide HAZ= coarse grain, less strength. Very narrow HAZ= fine grain but no ductility. Both could be good or bad, depends. HAZ variation depends on heat input and on how steady you travelled.The "Tooth" part is where the material pulled apart like pulling a dough ball apart (with the grain). There seems to be some deformation near the seam so that's good. With a "big eye" and ability to check hardness one can determine if you loitered in a spot and moved too quickly forward for a while, etc.Similar to above advice, practice makes smooth, smooth has a better chance to repeat (good or bad, but at least you know). I don't want to go to that "makes perfect" thing.Matt Attached Images
Reply:Originally Posted by Matt_MaguireYou can do testing like that with accurate load sensing and the results are likely to have a large scatter plot. Best to control one thing at a time... pick -> design, material, process.Then, when and if, you do tear it apart there is more to look at than just the welding part. The steel mill has tolerance, the rolling process has tolerance, the seam weld, and on and on. Stuff can creep in most anywhere.I up-sized the picture and see what looks like a "tooth" (arrow), this is good. I also think the failure is not exactly a straight line perpendicular to  tension. The HAZ is affected by heat input, slower travel = HAZ farther away and wider, faster travel = closer HAZ and narrow. Wide HAZ= coarse grain, less strength. Very narrow HAZ= fine grain but no ductility. Both could be good or bad, depends. HAZ variation depends on heat input and on how steady you travelled.The "Tooth" part is where the material pulled apart like pulling a dough ball apart (with the grain). There seems to be some deformation near the seam so that's good. With a "big eye" and ability to check hardness one can determine if you loitered in a spot and moved too quickly forward for a while, etc.Similar to above advice, practice makes smooth, smooth has a better chance to repeat (good or bad, but at least you know). I don't want to go to that "makes perfect" thing.Matt
Reply:Sorry for seeing this a bit late. a question to the original poster. Did you have a solid bar run through the top horiz. tube when you pushed it apart? If not I see what would concern me as a serious lack of deformation. With .035 that "tee" should have deformed over past 45 degrees before a rupture would even start. Dave makes a point about PWHT that should be listened to and perhaps experimented with on your end. In the end remember this, properly welded 4130 will bend and tear, not break.
Reply:If you look around the internet you will see all kinds of posts concerning welding Chrome Moly tubing.  There is even two schools of thought on whether TIG is better or worse than Oxy -acetylene welding.   The example you show is good in that is proves the cautions about heat affected zones being critical when welding alloy steels.  It fractured next to a weld that was not your best in the test piece.    In some cases if you are looking for "safer"  mild steel tubing bends and deforms considerably more before failure.  In some designs this is a bonus.  An example is the use of chain that is low alloy and not the best high tensile steel.  Before failure the links stretch and in some cases actually jam giving the people around an indication that they overstressed the chain.    High tensile strength alloys are not as ductile and are less likely to give warning signs before fracture.     For this reason sometimes it is wise to make things out of low carbon steel materials because they bend and stretch more before failure.
Reply:My opinion=if that was a failure on an actual bicycle, the rider would be dead or seriously injured from the collision, not from the welding process. I'd ride it.Two turn tables and a microphone.
Reply:Originally Posted by lotechmanIf you look around the internet you will see all kinds of posts concerning welding Chrome Moly tubing.  There is even two schools of thought on whether TIG is better or worse than Oxy -acetylene welding.   The example you show is good in that is proves the cautions about heat affected zones being critical when welding alloy steels.  It fractured next to a weld that was not your best in the test piece.    In some cases if you are looking for "safer"  mild steel tubing bends and deforms considerably more before failure.  In some designs this is a bonus.  An example is the use of chain that is low alloy and not the best high tensile steel.  Before failure the links stretch and in some cases actually jam giving the people around an indication that they overstressed the chain.    High tensile strength alloys are not as ductile and are less likely to give warning signs before fracture.     For this reason sometimes it is wise to make things out of low carbon steel materials because they bend and stretch more before failure.
Reply:Wouldn't those beads be smaller on .035" wall? Not criticizing, I don't know tig from pig. That why it's too hot?LibertarianLincoln AC/DC 225Everlast PowerPlasma 70 Hobart IronmanEverlast PowerTig 200DX
Reply:too much heat because its too cold...the beads are clearly cold..so you probably overheated  the metal because you sat too long in one spot..and probably a lot to do with too long an arc length, not the setting on the amp knob...